1. Field of the Invention
The present invention relates to an image data transmitting/receiving apparatus applied to an image forming apparatus of a type that receives, e.g., externally supplied image data by using an internally generated video clock.
2. Description of the Related Art
Recently, image forming apparatuses, e.g., laser printer units, are connected to various types of external output units (host units) to perform printing. Image data supplied from the host unit through a cable is input to a laser printer unit body through an external unit controller mounted to the laser printer unit.
When the laser printer unit starts an image forming operation, image data supplied from the host unit through the external controller is synchronized with a video clock generated in the controller of the laser printer unit, thereby forming the image. A video clock of this type is described in Japanese Laid-open Patent Publication (Kokai) No. 51-46141. More specifically, a video clock generated in the controller of a laser printer unit is supplied to an external unit controller. The external unit controller sends image data in response to the supplied video clock, so that the laser printer unit forms an image.
However, due to elements and the like in the external unit controller, the output timing of the image data is delayed from the video clock, and a phase difference occurs between the image data and the video clock. This phase difference differs from one external unit controller to another.
In order to eliminate the phase difference, video clocks generated in the controller are divided into those for outputting the image data by the external unit controller and those for forming an image by the laser printer unit. Synchronized adjustment of the image data is performed by changing the count of image-forming video clock output to the external unit controller or adding a signal adjusting section, e.g., a delay element, to the image data output section. However, it is cumbersome to change the image video clock count or to add the signal adjusting section, leading to an increase in cost.